Semi-automatic firearms, such as semi-automatic rifles, are described as being "semi-automatic" because the firing is done by a trigger and hammer mechanism in a manner that a new cartridge, or round, is loaded into the firing chamber from a clip contained within the rifle by action of the firing mechanism after each shot without the need for the rifleman to operate a loading device or lever. With the semi-automatic operation, the gun is cocked, ready for the next shot, which may then take place only upon the next pull of the trigger. The trigger must be pulled to fire each shot. In an automatic weapon, the gun will automatically load and fire each succeeding round as long as the trigger is held in the firing position.
The most widely-known semi-automatic rifle has been the U.S. .30 caliber M-1 rifle, or Garand, invented by John C. Garand, and described in his U.S. patents.
The Garand rifle, as with any other mechanical device, includes all its parts manufactured within certain tolerance limits. As a result, each rifle is minutely different in operation of the firing mechanism, particularly in the action of the trigger in what is commonly referred to as "creep".
"Creep" refers to the movement of the trigger just before firing. An undesirable amount of creep is responsible for a reaction by the rifleman for what is called "flinching", a nervous reaction by the rifleman to an anticipation of the instant of firing.
If a rifleman has had long experience with his own rifle, he will usually adjust intuitively to the action of his own rifle. Whereas, if the rifleman is given a different weapon of the same type of fire, he might experience a period of poor shooting because of his lack of familiarity with the different weapon. The "creep" might be slightly different and he might find himself instinctively flinching.
Normally, the rifleman is trained to ignore creep and to devote all his attention to the target, squeezing the trigger only when the target is lined up with the sights of the rifle, so that he will not be aware of the instant of firing.
In the Garand rifle as originally supplied, the trigger pull is indicated as being from 51/2 to 71/2 pounds. The typical trigger creep of the Garand is usually within the range of 0.01 to 0.02 inch.
Other devices have been invented to offer some control of trigger creep. I have found in the prior art the following U.S. patents for these various devices for adjusting trigger movement and for different forms of trigger mechanisms:
______________________________________ U.S. Pat. No. 2,377,338 Garand June 5, 1945 U.S. Pat. No. 2,399,253 Reilly April 30, 1946 U.S. Pat. No. 2,464,418 Sefried, II March 15, 1949 U.S. Pat. No. 2,550,280 Martin et al April 24, 1951 U.S. Pat. No. 2,590,862 Hoppert April 1, 1952 U.S. Pat. No. 2,873,650 Pinkerton, Jr. Feb. 17, 1959 U.S. Pat. No. 3,377,731 Lawrence April 16, 1968 U.S. Pat. No. 4,151,670 Rath May 1, 1979 ______________________________________
The patent to Garand, U.S. Pat. No. 2,377,328, describes in detail the well-known firing mechanism of the M-1, or Garand, rifle.
Reilly, U.S. Pat. No. 2,399,253, describes a modified sear mechanism for the Garand rifle, intending to reduce "creep" by adjustment of the adjusting screw 13 mounted on the sear 12.
Sefried, II, U.S. Pat. No. 2,464,418, describes a fire-control mechanism combining with modified trigger components to provide a finger piece operable from the exterior of the fire-arm to permit the rifleman to operate the rifle as either a semiautomatic weapon or as an automatic weapon, as he chooses.
Martin et al, U.S. Pat. No. 2,550,280, describes another type of semi-automatic rifle.
Hoppert, U.S. Pat. No. 2,590,862, describes a trigger mechanism for a Garand rifle which is intended to substantially eliminate the amount of creep characteristic of the weapon. A spring is mounted in back of the primary sear and secured to the back of the trigger. The tension of the spring against the sear is adjusted by means of a screw acting against the rear of the spring.
Pinkerton, U.S. Pat. No. 2,873,650, describes a fluid-operated system adapted to a Grand rifle for converting the rifle to automatic firing.
Lawrence U.S. Pat. No. 3,377,731, describes a lever action system for a firearm.
Rath, U.S. Pat. No. 4,151,670, describes a firing mechanism for semi-automatic firearms which includes a safety device having an extension protruding inside the trigger guard to be felt by the shooter so that he may easily determine whether the gun is cocked or not cocked.